2001 mazda protege DX
 

So i brought this car off this person. After a few months of driving it, it starts to make a screeching noise when I put it in reverse or in any gear when I initially first start it. The mileage is 48,000. My friend said it might be the timing belt, online said it might be the torque converter bolts and someone at work said it might be the alternator belt since timing belt don't make noises. Can anyone help me with suggestions here? and any really good hot to video's or step by step process on changing any of these would be greatly appreciated since i am new to cars and want to learn some mechanical stuff.

I would change all rubber fan belts. Your car is definitely old enough and enough miles on it. Inspect tensioner and pulleys as well.

Indeed!
Go to Youtube and search. There are lot s of how to videos and these jobs are almost all the same for similar cars of various makes.